1. Field of the Invention
The present invention relates to a process for producing an alkali metal styrenesulfonate by extracting from an aqueous solution containing an alkali metal halide and an alkali metal styrenesulfonate, and back-extracting styrenesulfonic acid anions.
2. Description of the Prior Art
In the past, styrenesulfonates have been produced by sulfonating a halogenoethylbenzene with chlorosulfonic acid or sulfur trioxide and reacting the resulting halogenoethylbenzenesulfonyl chloride or halogenoethylbenzenesulfonic acid with an alkali metal hydroxide in water to dehydrohalogenate the sulfonic acid or sulfonyl chloride to the product styrenesulfonate as shown by the reaction formulae (1) and (2). After the reactions the product is obtained by crystallizing the crude product and then filtration. ##STR1## wherein M represents an alkali metal such as K, Na or Li and X represents a halogen such as C1 or Br.
However, the conventional process has various technical problems. For example, the desired alkali metal styrenesulfonate product is highly soluble in water, and consequently it is necessary to minimize the quantity of water used as a solvent. On the other hand, if the quantity of water used is too small, stirring of the reaction mixture containing precipitated material is difficult. The reaction can be effectively conducted at temperatures higher than 100.degree. C to improve crystallization of the product. However, if the temperature is too high, control of the reaction is difficult under the boiling conditions, and the type of reactor material is limited so that it can withstand the aqueous caustic alkali solution at high temperatures.
A need, therefore, continues to exist for a method of preparing styrenesulfonates which overcomes the problems of the prior art procedures.